Eddy current testing is a non-destructive testing (NDT) inspection method used for a variety of purposes, including for flaw detection, material and coating thickness measurements, material identification and establishing the heat treatment condition of certain materials.

What Is Eddy Current Testing?

Eddy current testing is one of several non-destructive testing methods that uses the electromagnetism principle for flaw detection in conductive materials. A specially designed coil energised with an alternating-current is placed in proximity to the test surface, generating a changing magnetic field that interacts with the test-part and produces eddy currents in the vicinity.

Variations in the changing phases and magnitude of these eddy currents are then monitored through the use of a receiver-coil or by measuring changes to the alternate current flowing in the primary excitation-coil.

The electrical conductivity variations, the magnetic permeability of the test-part, or the presence of any discontinuities, will cause a change in the eddy current and a corresponding change in phases and amplitude of the measured current. The changes are shown on a screen and are interpreted to identify defects.

Advantages

• Able to detect surface and near-surface cracks as small as 0.5mm
• Able to detect defects through several layers, including non-conductive surface coatings, without interference from planar defects
• Non-contact method making it possible to inspect high-temperature surfaces and underwater surfaces
• Effective on test objects with physically complex geometries
• Provides immediate feedback
• Portable and light equipment
• Quick preparation time – surfaces require little pre-cleaning and couplant is not required
• Able to the measure electrical conductivity of test objects
• Can be automated for inspecting uniform parts such as wheels, boiler tubes, or aero-engine disks

Applications

• Inspection of parts or components including:
  Welded joints
  Bores of in-service tubes
  Bores of bolt holes
  Metal tubes
  Friction stir welds
  Gas turbine blades
  Nozzle welds in nuclear reactors
  Hurricane propeller hubs
  Cast iron bridges
  Gas turbine blades